Method and apparatus for measuring thickness of a layer in a multi-layered object

Abstract

A method and device for determining a thickness of a layer in an object. For each of a plurality of frequencies, a continuous vibrational wave is generated at a surface of the layer and an energy of a steady state echo wave produced in the object in response to the generated vibrational wave is measured. The thickness of the layer is then calculated based upon the measured energies of the steady state echoes.

What is claimed is:  
     
       1. A method for determining a thickness x 1  of a layer in an object, the method comprising the steps of: 
       (a) for each of plurality of frequencies f 1 , . . . f k    
       (aa) generating a continuous vibrational wave at a surface of the layer;  
       (ab) measuring an energy of a steady state echo wave produced in the object in response to the generated vibrational wave;  
       (b) calculating the thickness of the layer based upon the measured energies of the steady state echo waves.  
     
     
       2. The method of  claim 1 , further comprising a step of determining two or more frequencies f n1 , f n2 , . . . f nj  among the frequencies f 1  . . . f k  at which the energy of the steady state echo wave has a local minimum. 
     
     
       3. The method of  claim 2 , wherein the thickness is calculated based upon the two or more frequencies f n1 , f n2  . . . f nj . 
     
     
       4. The method of  claim 3 , wherein the number of frequencies at which the energy of the steady-state echo has a local minimum between f n1 , and f n1+1  is a constant m for all 1 between 1 and j−1. 
     
     
       5. The method according to  claim 4 , wherein the constant m is zero. 
     
     
       6. method of  claim 4  wherein the thickness of the layer is calculated based upon the ratios            f   n2       f   n1       ,         f   n3       f   n2                     …                       f   nj       f     nj   -   1         .                       
     
     
       7. The method of  claim 6 , wherein calculation of the thickness involves solving the over determined system of equations for n 1             f   n2       f   n1       =         2        (       n   1     +   m   +   1     )       -   1         2        n   1       -   1                   f   n3       f   n2       =         2        (       n   1     +     2      m     +   1     )       -   1         2        (       n   1     +   m   +   1     )       -   1             ⋮             f   nj       f     nj   -   1         =           2        (       n   1     +       (     j   -   1     )        m       )       -   1         2        (       n   1     +       (     j   -   2     )        m     +   1     )       -   1       .                     
     
     
       8. The method of  claim 7 , wherein the thickness x 1  is calculated according to the algorithmic expression:            x   1     =         (       2        n   1       -   1     )        c       4        f   n1           ,                   
       where c is a speed of the waves in the layer. 
     
     
       9. The method of  claim 6 , wherein calculation of the thickness involves solving the over determined system of equations for n 1             f   n2       f   n1       =         n   1     +   m   +   1       n   1                   f   n3       f   n2       =         n   1     +     2      m     +   1         n   1     +   m   +   1             ⋮             f   nj       f     nj   -   1         =           n   1     +       (     j   -   1     )        m     +   1         n   1     +       (     j   -   2     )        m     +   1       .                     
     
     
       10. The method of  claim 9 , wherein the thickness x 1  is calculated according to the algorithmic expression: 
       
         
             x   1   n   1   c/ /2 f   n1 ,  
         
       
       where c is a speed of the waves in the layer. 
     
     
       11. A method for detecting the thickness of a bone, in an organism the method comprising the steps of: 
       (a) for each of a plurality of frequencies f 1 , . . . f k    
       (aa) generating a continuous vibrational wave at a surface of the bone;  
       (ab) measuring an energy of a steady state echo wave produced in the organism in response to the generated vibrational wave;  
       (b) calculating the thickness of the bone based upon the measured energies of the steady state echo waves.  
     
     
       12. A device for determining a thickness of a layer in an object, the device comprising: 
       (a) a transducer configured to generate a plurality of input vibrational wave pulses;  
       (b) a receiver configured to receive a steady-state echo wave produced by an input vibrational wave pulse;  
       (c) a probe configured to transmit a vibrational wave from the transducer to a surface of the layer and to transmit the steady-state echo wave from the surface to the receiver;  
       (d) a processor configured to  
       (da) determine a frequency of each of the plurality of input vibrational waves;  
       (db) store in a memory an energy of each of a plurality of steady-state echo waves; and  
       (dc) calculate the thickness based upon the stored energies of the steady-state echo waves; and  
       (e) a display configured to display the thickness.  
     
     
       13. The device according to  claim 12 , wherein the probe has an acoustic impedance Z in  satisfying Z in >Z i , wherein Z i  is an acoustic impedance of the layer. 
     
     
       14. The device according to  claim 13 , wherein Z in  further satisfies                Z   1     +         Z   2          Z   in         Z   1         〉          Z   2          Z   in       ,                   
       wherein Z 2  is the acoustic impedance of a region of the object juxtaposed to the layers. 
     
     
       15. The device according to  claim 13 , wherein Z in  further satisfies                  Z   2     +     Z   in       〉          Z   1       +         Z   2          Z   in         Z   1         ,                   
       wherein Z 2  is the acoustic impedance of a region of the object juxtaposed to the layer. 
     
     
       16. A device for determining a thickness of a bone in an organism, the device comprising: 
       (a) a transducer configured to generate a plurality of input vibrational wave pulses;  
       (b) a receiver configured to receive a steady-state echo wave produced by an input vibrational wave pulse;  
       (c) a probe configured to transmit a vibrational wave from the transducer to a surface of the bone and to transmit the steady-state echo wave from the surface to the receiver;  
       (d) a processor configured to  
       (da) determine a frequency of each of the plurality of input vibrational waves;  
       (db) store in a memory an energy of each of a plurality of steady-state echo waves; and  
       (dc) calculate the thickness based upon the stored energies of the steady-state echo waves; and  
       (e) a display configured to display the thickness.